This invention relates generally to an auxiliary switch for electrical power distribution interruption equipment and more particularly to an auxiliary position switch for electrical circuit breakers that provides a signal indicative of the position of the contacts of the circuit breaker.
Electrical circuit breakers are utilized throughout electrical power transmission and distribution systems to interrupt the flow of electric current to a protected load. A conventional circuit breaker includes a pair of separable contacts that open in response to a fault condition, e.g. overcurrent and ground fault, to interrupt the current flow. Auxiliary position switches are typically mounted to the frame of the circuit breaker to provide an electrical signal indicative of the position of the circuit breaker contacts.
A typical auxiliary switch includes a movable contact structure in which one contact is disposed at a stationary contact arm, while the other contact is disposed on a movable contact arm. A spring generally urges the movable contact arm about a pivot to position the movable contact arm in a normally open or normally closed state. A plunger engages the movable contact arm for opening the separable contacts in the normally closed configuration or for closing the separable contacts in the normally open configuration. When the plunger is depressed, it moves the movable contact arm to open or close the contacts accordingly.
Typically, a circuit breaker rod acts upon the plunger. The circuit breaker rod is mechanically linked to a movable contact arm of the circuit breaker to provide an indication of the position of the separable contacts (i.e., opened or closed). The circuit breaker rod is displaced upon rotation or displacement of the movable contact arm of the circuit breaker. The displacement of the circuit breaker rod in turn displaces the plunger of the auxiliary switch which provides an electrical signal to an external monitoring system indicative of the position of the contacts of the circuit breaker.
When using an auxiliary position switch with a circuit breaker, it is desirable to utilize a switch that does not exhibit contact bounce. Control circuits are sensitive and an intermittent breaker position signal could result in false signals. Auxiliary position switches that exhibit little or no contact bounce typically have been single action either normally open (N.O.) or normally closed (N.C.).
Depending upon the configuration of the external monitoring system, the configuration of auxiliary switch and the circuit breaker may be such that the auxiliary switch is normally open when the circuit breaker contacts are closed or normally open when the circuit breaker contacts are open. As one will appreciate, the configuration of the auxiliary switch (normally open and normally closed) is dependent upon the configuration of the circuit breaker and the external monitoring system. Accordingly, circuit breakers, including auxiliary switches, are provided for a number of configurations which require a number of auxiliary switches to be stocked for each configuration.
Circuit breakers may also be configured in the field. As a result of the number of different configurations for interconnecting the auxiliary switch to the external monitoring system, field personnel are required to carry a large inventory of auxiliary position switches of different types to provide the necessary configuration (i.e., normally open and normally closed) as described hereinabove. High inventories along with extensive preparation are, therefore, required for configuring auxiliary position switches.